Effect of Oxygen Tension on NMR Spin-Lattice Relaxation Rate of Blood in vivo

Abstract

Spin-lattice relaxation rate (1/T1) was measured in the left (LV) and right (RV) ventricular cavities in four conscious normal humans and four anesthetized greyhound dogs breathing spontaneously. Inspired oxygen concentration (FIO2) was varied in five steps from 21 to 100%. In dogs, blood was sampled from indwelling catheters in the pulmonary artery and aorta for measurement of PO2. Saturation-recovery and inversion-recovery tomographic images of the ventricular cavities were obtained supine during quiet breathing using a whole-body NMR scanner operating at a static magnetic field strength of 0.15 Tesla. From FIO2 21 to 100%, 1/T1 of LV increased by 11.6% in humans and 9.6% in dogs. In dogs, 1/T1 increased by 2.8% per 100 mm Hg increase in aortic PO2 (r greater than 0.87). There was no correlation in dogs between 1/T1 in RV and pulmonary artery PO2. The LV/RV 1/T1 ratio in dogs increased by 4% per 100 mm Hg increase in the LV-RV PO2 difference, and by 8% in humans as FIO2 increased from 21 to 100%. A rise in dissolved oxygen concentration increases NMR spin-lattice relaxation rates of blood in vivo to a small but significant extent.